Serious damage can result to homes or structures that incorporate a liquid heat transfer system should the system be breached, either by a slow leakage loss over a long period of time, or by a sudden catastrophic breach of the system. Typical hydronic systems incorporate a boiler feed valve with a backflow preventer, to replace normal water volume losses, which has a component caused by air coming out of solution and being removed by an air separator. A bladder type expansion tank modulates volume due to temperature changes, to maintain system pressure within a narrow range, and will only accommodate very minor actual loss of water volume. The feed valve adds water if and when the system falls below the normal operating set pressure. It is common to operate the system with this feed valve supplied at all times by the incoming water supply line, so that make-up water can be added as called for.
A very slow leak that develops anywhere in the system may cause a continual water loss less than the rate of fill, and thus may continue for an extended period of time, resulting in possibly hidden and possibly severe water or mold damage before the leak is discovered, even though the heating system may continue to provide heat as usual. A sudden catastrophic breach may result in a very large amount of water being released before discovery, particularly if the structure is not occupied at the time the breach occurs. If the feed valve is able to supply water at a rate at least equal to the rate of water loss, the system will continue to operate, but at greatly diminished heat output and all the while discharging large volumes of water into the structure. With heating disabled, the structure may fall below freezing temperature inside, leading to further damage to the heating and or plumbing systems.
It is a practice of some heating equipment installers to operate a newly filled system for a certain period of time, to remove the bulk of the air in solution, and then close the incoming water supply to the feed valve. This has the effect of limiting possible water release to the amount of water contained within the system, assuming any breach is at the lowest point, or to the amount of water released to bring system pressure to either zero, or to the point of activating a low water cutoff or a low pressure shut-off, either of which may be incorporated in the heating appliance. In a typical medium size residence, the volume loss to reduce pressure to that of static head may be as little as 16 fluid ounces.
This approach of isolating the system prevents catastrophic water damage to the structure, but a very slow leak may reduce system pressure to the point that the circulator pump will cavitate due to insufficient pressure to maintain fluid on the suction side. At that point, it is likely that the pump will burn out due to running dry because of an unsatisfied call for heat. The safety shutoffs on the appliance may or may not come into play, and the likely first warning of a problem is a drop in temperature in the structure, with no readily observable cause. A structure space temperature monitoring system may only be activated after there is a circulator pump failure, necessitating replacement of now failed equipment, which can be problematic during nights and holidays.
Water sensor monitoring systems well known in the prior art have the limitation that they will only detect fluid loss at the location of the sensor. The most damaging leaks in hydronic systems occur at locations remote from the appliances, usually within wall or floor assemblies, and are not initially readily observed until there is a significant water loss and or consequent damage. Water flow monitoring systems are employed as whole-house domestic water system leak detectors. These systems cannot adequately protect the hydronic heating system in an occupied structure. The allowable flow levels must of necessity be far greater than the smallest potential leaks in the hydronic system. If a flow-monitoring detector is dedicated to the hydronic system, that system must be continuously open to supply pressure, in order to detect a flow condition. The detector must then decide if flow is excessive, and actively close off the supply water. Very low leakage rates may be below the sensitivity of such detectors, or less than the allowable volume for a given time period.
If a hydronic system is closed off from the supply water source, it is possible for leakage to disable the circulator pump without any flow being indicated by the detector. A hydronic system requires only a minimum pressure to maintain function. Monitoring flow into the system must therefore infer a pressure condition in order to decide what protective actions to undertake. Heating systems may equally easily develop a leak in both occupied and unoccupied structures, whether in heating mode or during seasonal shutdown, so that a leak detector and safety shutdown must perform equally well under all these circumstances.
Infrared imaging cameras may be successfully used to locate leaks in a hot water heating system, which may occur within floor or wall assemblies, and are thus not readily observable. In typical trade practice, this method will only be employed after the likelihood of a leak has been established, which may come well after the initiation of a very slow and damaging leak into the structure.
An existing device has the primary purpose of a complete separation of the hydronic system from the domestic water supply. Make-up fluid is stored in a tank, and added to the hydronic system by a pump, which is controlled by a pressure switch. This allows for the use of fluids other than water. Leakage is measured indirectly, via an alarm signal when the storage tank is depleted. There may not be any notification of a very slow leak in the hydronic system until long after initiation, which may result in considerable hidden damage.
Another existing device monitors pressure in an isolated hydronic system, and in the most basic configuration, merely reports a drop in pressure to a preset warning level. It is the responsibility of the warning recipient to take an explicit action to add fluid to the system. An enhancement includes the ability to actively open a supply valve to restore pressure. This version will only warn of presumed leakage if the restore function happens too frequently in a given time period, and may allow for feeding of a very slow leak indefinitely, with consequent hidden damage as the result.
The increase in use of hot water radiant heating systems has resulted in an increase in a particularly insidious type of leak and subsequent water damage. These systems incorporate a large amount of water filled tubing directly under the subfloor, or even the flooring material itself. It is very easy to penetrate the tubing with a misplaced fastener, either during construction or after occupancy. Pneumatic staples and finish nails and drywall screws are the most likely culprits, and any may penetrate one wall or both sides of the tube. The penetration may be sealed by the tubing material sufficiently to hold pressure during a pressure test normally performed during the construction phase of the project.
A fastener may also penetrate and be sealed by the tubing after the system is filled and running, when a much lower operating pressure is in the system than during testing. In either case, the water in the heating system will start a slow process of corroding the fastener and or the aluminum layer of a Pex-AL-Pex tube. At some point, typically a number of months after start-up, water pressure will force its way around the degraded fastener, and a leak ensues.